Many pest control active ingredients cause irritation (paresthesia) to warm-blooded animals (including humans). This irritation to the skin and/or eyes of warm-blooded animals hampers the use of these pest control active ingredients. This irritation factor occurs even when the pest control active ingredient is blended with polymers or in other formulations (such as granules, dusts, dips, liquids, emulsions, etc.) wherein the active ingredient is considerably diluted.
The synthetic pyrethroid class of insecticides is known to cause paresthesia when coming into contact with the skin, with differing degrees of paresthesia being caused by different synthetic pyrethroids. Generally, the higher the degree of paresthesia, the more active the pyrethroid is against various insects; and those having a cyano group in their molecular structure produce a greater degree of paresthesia. While paresthesia is a transitory phenomenon, higher degrees of paresthesia have been known to cause severe trauma to animals' skins when applied thereto and have required days for the pain to end and weeks for the skin to repair. Thus, it has prevented some of the most beneficial efficacious pyrethroids from being used on animals due to the unacceptable dermatological effects produced on the animal.
Efforts to prevent or reduce the paresthesia effect of pyrethroids have been attempted with some success. However, in marketing these technologies to the total spectrum of the dog population, it was discovered that there is a small percentage of the total dog population, specifically the smallest dog breeds, that is more susceptible to pyrethroid-induced paresthesia than the general population and that this paresthesia in this group of small dogs is unacceptable.
It would be desirable to have a synthetic pyrethroid-containing product that not only reduces but actually eliminates paresthesia, including in the small dog breeds, and to have a liquid synthetic pyrethroid-containing product that would be suitable for treatment of small animals.